Implantable medical devices (IMDs) are devices designed to be implanted into a patient. Some examples of these devices include cardiac function management (CFM) devices such as implantable pacemakers, implantable cardioverter defibrillators (ICDs), cardiac resynchronization devices, and devices that include a combination of such capabilities. The devices are typically used to treat patients using electrical or other therapy or to aid a physician or caregiver in patient diagnosis through internal monitoring of a patient's condition. The devices may include one or more electrodes in communication with one or more sense amplifiers to monitor electrical heart activity within a patient, and often include one or more sensors to monitor one or more other internal patient parameters. Other examples of implantable medical devices include implantable diagnostic devices, implantable drug delivery systems, or implantable devices with neural stimulation capability.
Additionally, some IMDs detect events by monitoring one or more electrical heart activity signals. In CFM devices, these events include heart chamber expansions or contractions. By monitoring cardiac signals indicative of expansions or contractions, IMDs are able to detect heart chamber mechanical dyssynchrony, such as when the right ventricle and the left ventricle are not contracting in unison. Cardiac resynchronization therapy (CRT) may be provided to correct the cardiac dyssynchrony. Typically, IMDs that detect cardiac dyssynchrony look to cardiac events that are global to contractions of the heart, such as estimating heart chamber volumes for example. However, cardiac dyssynchrony may be difficult to define and determine.